Discuss What is a Z-line and Z-loop test? in the Electrical Forum area at ElectriciansForums.net

Welcome to ElectriciansForums.net - The American Electrical Advice Forum
Head straight to the main forums to chat by click here:   American Electrical Advice Forum

Are you talking about the options on a test device such as a mft?

If so, Z line measures the impedance Z of the lines R1 + Rn for phase to neutral, and R1 + R1 for phase to phase (depends on your connection)

Z loop measures the impedance of the earth loop - R1 + R2 (line and earth connection)
 
Or is the OP asking why such tests are done?

If so, the Z-loop test is to prove the fault current in the event of phase-earth short is sufficiently high to operate the over-current protective device (OCPD) fast enough to have an acceptably low risk of electric shock, or conductor overheating. In a typical UK case (230V, TN system) the "fast enough" is 0.4s for most circuits, 5s for some feeders, etc.

The Z-line test is done as well so the higher of the two prospective fault currents can be recorded, and compared with the ratings of equipment to establish that in the event of a short the OCPD and/or switch-gear can safely interrupt it.
 
Are you talking about the options on a test device such as a mft?

If so, Z line measures the impedance Z of the lines R1 + Rn for phase to neutral, and R1 + R1 for phase to phase (depends on your connection)

Z loop measures the impedance of the earth loop - R1 + R2 (line and earth connection)
More of a basic question like, "Why do we do a Z-line or Z-loop test?"
 
More of a basic question like, "Why do we do a Z-line or Z-loop test?"

As said by pc above, there are two basic reasons, firstly to ensure the impedance is low enough that sufficient current flows in the event of a fault and therefore will operate the protection within the required disconnection times.

Secondly, to determine how much current could flow as a maximum, to ensure that the fault level is not higher than the equipment can withstand or open where appropriate.

There are two basic possibilities, a fault involving earth, and a fault between phases or phase and neutral therefore both have to be checked
 

Reply to What is a Z-line and Z-loop test? in the Electrical Forum area at ElectriciansForums.net

OFFICIAL SPONSORS

Electrical Goods - Electrical Tools - Brand Names Electrician Courses Green Electrical Goods PCB Way Electrical Goods - Electrical Tools - Brand Names Pushfit Wire Connectors Electric Underfloor Heating Electrician Courses
These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then CLICK HERE and post a thread with who you are, and we'll send you some stats etc

Electrical Forum

Welcome to the Electrical Forum at ElectriciansForums.net. The friendliest electrical forum online. General electrical questions and answers can be found in the electrical forum.
This website was designed, optimised and is hosted by Untold Media. Operating under the name Untold Media since 2001.
Back
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.

I've Disabled AdBlock